It is sometimes observed in conventional catalytic converters that the catalyst bed is subjected to a sagging phenomenon especially of a portion thereof remote from a portion which is directly connected to some rigid member of the converter. This is because the exothermic reaction of the catalyst pellets gives off a great amount of heat which causes the bed to be heated at a high temperature ranging from about 700.degree. C. to 900.degree. C., so that the bed is subjected to considerable volume expansion. Furthermore, under such high temperatures, the bed is curved or bent downwardly at the unsupported portions thereof because of weight of the catalyst therein. This phenomenon becomes more critical when the catalyst bed is formed with outwardly projecting louvers.
In the case that the catalyst bed is expanded, the catalyst pellets in the bed can become loose thus causing the mutual abrasion of same to produce ultrafine catalyst powder which will cause the so-called secondary air-pollution problem. Furthermore in this case, the flow resistance of the converter is increased because the downstream passage of the converter is critically limited by the sagging of the expanded catalyst bed.
Although stud bolts for firmly connecting the catalyst bed to the container of the converter can be used, the flow resistance of the converter is considerably increased by the provision of same, acting in this instance as flow restrictors.